Heat oil in a 12-inch nonstick skillet over medium-high heat until it shimmers. Add the onion and cook until softened and starting to brown, 5 to 7 minutes. Stir in the corn and cook until the kernels are lightly toasted, about 4 minutes. Stir in the rice, garlic, cumin, and cayenne and cook until the garlic is fragrant.

Pour in the broth and bring the mixture to a simmer. Cover the pan tightly, reduce the heat to medium-low, and simmer gently for 25 minutes, giving it a stir once or twice to ensure even cooking.

Stir in the beans, recover the pan, and continue to simmer until the liquid has been fully absorbed and the rice is tender, 20 to 25 minutes. Season with salt and pepper to taste.

Whisk the remaining oil, tomatoes, scallions, cilantro, and lime juice in a small bowl and season with salt and pepper. Sprinkle the fresh tomato mixture over the rice and beans and serve while the rice is hot and the salsa is bright.